Linux

System

• Host information, kernel and OS version etc: hostnamectl
• Shell type: echo %0
• Review environment variables:
  • printenv
  • env
• Reboot: sudo reboot
• Latest restart time: uptime
• All processes info: ps -ef or ps aux
• Specific process info: ps -p <pid> -o pid,vsz=MEMORY -o user,group=GROUP -o comm,args=ARGS
• Show the kernel message buffer since the latest reboot: dmesg -T
• Monitor system activity real-time: joiurnalctl -f
  • Monitor kernel messages: joiurnalctl -fk

systemctl

• Configuration location: /etc/systemd/system/
• List of units: sudo systemctl list-units --all
  • Mark inactive units: sudo systemctl list-units --all --state=inactive

CPU

Memory

Disk

Network

Navigation and Search

• Show only directories: ls -la | grep "^d"
• Find file by name:
  • from current directory: find . -name "docker-compose*"
  • from the root: find / -name "docker-compose*"
• Find the program location: which python3 or type -a python3 or command -v python3
• Recursive search in files starting from current directory: find . -name "*.ts" -exec grep -H "extends Assignable" {} +
• Search with regular expression: grep -iE "cpu|disk| *

Users and groups

• The users/groups configuration file: /etc/group
• List of users: sudo cat /etc/group
• List of groups: groups
• Users in a group: grep docker /etc/group
• Create new user: sudo adduser sol
• Add user to a group: sudo usermod -aG docker andrei
  • Add user to the sudoers group:sudo usermod -aG sudo andrei
  • Confirm that the user was added to a group: groups andrei
• Swith to root: su -
• Change owner recursively: sudo chown -R newuser:newgroup /mnt/data
• Show currently connected users: who

SSH

• Install openssh-server to allow SSH access:
  1. sudo apt-get update
  2. sudo apt-get install openssh-server
  3. Start the server sudo service ssh start or sudo systemctl start ssh
• Generate SSH key for the new user on the client machine: ssh-keygen -t rsa -b 4096 -C "your_email@example.com"
• Configure SSH key based authentication: run ssh-copy-id username@host on the client machine.

Archiving

• Archive files: tar -cvzf archive.tar.gz file1 file2
• Archive directory: tar -czvf archive-name.tar.gz /path/to/directory
• View the archive contents: tar -tvf archive.tar.gz
• Test the archive:
  • zst: zstd --test archive.tar.zst
• Extract:
  • bz2 archive: tar -xjf archive.tar.bz2
  • gz archive: tar -xvf archive.tar.gz
  • zst archive: tar --use-compress-program=unzstd -xvf archive.tar.zst
• Install application from the .deb archive: sudo dpkg -i your-package-name.deb

Symbolic Links

• Create symbolic link to file: ln -s ../../../../../cpp/common/messaging/sbe/me/me.xml .
• Create symboli link to directory: ln -s /path/to/src_directory ~/symlink_directory

Data transfer

• Copy file from host: scp andrei@64.233.160.01:/home/andrei/data/account_update.json .
• Copy directory from host: scp -r sol@64.233.160.01:/home/andrei/data/ .
• Copy file to network host: scp account_update.json andrei@64.233.160.01:/home/andrei/data
• Copy directory to network host: scp -r data andrei@76.16.6.193:/tmp

Other

• Generate UNIX Timestamp: date +%s
• Change time zone:
  1. Check the current timezone: timedatectl
  2. Set timezone to UTC: sudo timedatectl set-timezone UTC
• Rotate logs: logrotate /etc/logrotate.hourly.d/containers
• Convert HEIC images to JPEG: install and use the heif-convert` converter.